Belt conveyors are used for transporting a wide range of materials, such as coal, limestone and ore. Some of the material carried by the material-conveying stretch of the belt sticks to the belt. The return stretch of the belt is commonly equipped with a belt cleaner, to remove the stuck material.
One highly effective belt cleaner is a ribbed roller; the roller is driven at a speed such that the ribs of the roller act somewhat as scrapers; the roller is supported so that the edges of the ribs sweep along the surface of the belt.
An early example of belt cleaner is described in U.S. Pat. No. 2,652,920. There, a rotor that has rubber belt-cleaning blades is supported for rotation on a pair of pivoted arms. The rotor's axis is fixed, and the arms are adjustable. While not stated, the rubber blades can yield to accommodate thickened portions of the belt such as the splice that forms the belt into an endless loop.
Rollers having ribs of hard material are more effective as cleaners; the ribs act like scrapers. U.S. Pat. No. 3,583,555 describes a belt cleaner having a ribbed cleaning roller of hard material. The roller is supported on a pair of pivoted arms and the arms are spring-biased so that the roller's axis is movable toward and away from the conveyor belt. The mean position of the roller is maintained by a balance of opposite-acting pairs of springs. One of the roller-supporting arms carries a motor-and-belt drive. The roller and the motor have substantial weight. In that construction, the roller is prone to bounce entirely away from the belt when local thickening of the belt is encountered. Moreover, because the roller is spring-biased to a neutral position, the effectiveness of the ribs as scrapers is inherently limited. Only a weak spring force can be allowed to hold the ribs of the roller in position to sweep along and clean the belt's surface. If the adjustment were to maintain firm force to the roller holding the ribs firmly against the belt, the cleaning would be effective but the ribs would wear away rapidly.
U.S. Pat. No. 5,161,666 describes another belt cleaner having a ribbed roller supported by springs that balance the weight of the roller and its drive, the whole being adjustable so that the ribs can sweep along the belt surface. If the roller were biased firmly against the belt, the ribs would act more effectively as scrapers. However, the ribs would wear away rapidly, because the ribs are driven at high speed along the belt surface. As in U.S. Pat. No. 3,583,555, the spring bias balances the weight of the roller, the motor, and any other associated weight. In the neutral condition of the springs, there is theoretically no bias restraining the cleaning roller in position for the ribs to sweep along the belt's surface for cleaning the belt.